Temperature-Dependent Chemical Functional Group Reorientation at Silicone Surfaces

The structure of silicone polymer surfaces at elevated temperatures is of interest to industrial applications such as sealants and electrical insulators, and for scientific studies including the thermal control of droplets in microfluidic devices. Nonlinear vibrational spectroscopy has been used to study the temperature-dependent surface structure of poly(dimethylsiloxane) when exposed to water and a perfluorinated hydrophobic liquid. Quantitative analysis of the methyl plane orientation was performed using a combination of peak ratios and peak amplitudes that enable the proposed structures to be identified. For both environments, the tilt and twist of the methyl plane was found to increase with temperature in a reversible manner. This has been attributed to be a consequence of the backbone reorganization due to temperature-dependent density changes.